System, method and apparatus for laser produced plasma extreme ultraviolet chamber with hot walls and cold collector mirror

ABSTRACT

A system and method for an extreme ultraviolet light chamber comprising a collector mirror, a cooling system coupled to a backside of the collector mirror operative to cool a reflective surface of the collector mirror and a buffer gas source coupled to the extreme ultraviolet light chamber.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims priority from U.S.patent application Ser. No. 12/725,167 filed on Mar. 16, 2010 andentitled “System, Method and Apparatus for Laser Produced Plasma ExtremeUltraviolet Chamber with Hot Walls and Cold Collector Mirror,” which isincorporated herein by reference in its entirety. This application alsoclaims priority through application Ser. No. 12/725,167 from U.S.Provisional Patent Application No. 61/168,033 filed on Apr. 9, 2009 andentitled “Extreme Ultraviolet Light Output,” which is incorporatedherein by reference in its entirety for all purposes. This applicationalso claims priority through application Ser. No. 12/725,167 from U.S.Provisional Patent Application No. 61/168,012 filed on Apr. 9, 2009 andentitled “System, Method and Apparatus for Laser Produced Plasma ExtremeUltraviolet Chamber with Hot Walls and Cold Collector Mirror,” which isincorporated herein by reference in its entirety for all purposes. Thisapplication also claims priority through application Ser. No. 12/725,167from U.S. Provisional Patent Application No. 61/168,000 filed on Apr. 9,2009 and entitled “System, Method and Apparatus for Droplet Catcher forPrevention of Backsplash in a EUV Generation Chamber,” which isincorporated herein by reference in its entirety for all purposes.

BACKGROUND

The present invention relates generally to laser produced plasma extremeultraviolet systems, methods and apparatus, and more particularly, tosystems, methods and apparatus for droplet management in a laserproduced plasma extreme ultraviolet system.

Laser produced plasma (LPP) extreme ultraviolet (EUV) systems produce aplasma by irradiating a droplet of a plasma target material with asource laser. The resulting plasma emits light at a desired wavelength,in this instance, EUV (e.g., less than about 50 nm wavelength andincluding light at a wavelength of about 13.5 nm or less).

Unfortunately irradiating the droplet of the plasma target material canresult in debris from the droplet. The debris can be deposited on thecollector mirror and other inner surfaces of the EUV chamber. The debrisdeposited on the collector mirror can reduce the amount of EUV lightoutput.

Further, some of the droplets of the target material are not irradiatedby the source laser and as a result may produce splashes and othermicro-particles and debris that can become deposited on the innersurfaces of the LPP chamber.

In view of the foregoing, there is a need for providing better controlof the micro-particles and debris generated during the process ofoperating in a LPP EUV chamber.

SUMMARY

Broadly speaking, the present invention fills these needs by providingan improved EUV light chamber in an LPP EUV system. It should beappreciated that the present invention can be implemented in numerousways, including as a process, an apparatus, a system, computer readablemedia, or a device. Several inventive embodiments of the presentinvention are described below.

One embodiment provides an extreme ultraviolet light chamber comprisinga collector, a cooling system coupled to a backside of the collectoroperative to cool a reflective surface of the collector and a buffer gassource coupled to the extreme ultraviolet light chamber.

The chamber can also include a target material condenser system coupledto the extreme ultraviolet light chamber. The chamber can also includemultiple baffles located between the collector and an output of theextreme ultraviolet light chamber. The chamber can also include a heatsource coupled to at least a portion of the baffles. The heat source canbe capable of heating at least a portion of the baffles to a temperaturegreater than the reflective surface of the collector. The heat sourcecan be capable of heating at least a portion of the baffles to a meltingtemperature of a target material.

At least a first portion of each one of the baffles can be substantiallyaligned to an irradiation region. At least a second portion of at leastone of the baffles is substantially not aligned to the irradiationregion. The baffles can begin at an edge of a transmissive region andthe baffles extend to an inner surface of the extreme ultraviolet lightchamber. Each one of the baffles is separated from an adjacent baffle bya corresponding space. Each one of the corresponding spaces between theadjacent baffles can have an equal width or a different width.

The chamber can also include a target material condenser system coupledto the extreme ultraviolet light chamber. The target material condensersystem can include a vacuum source coupled to the extreme ultravioletlight chamber.

Another embodiment provides an extreme ultraviolet light chamberincluding a collector and multiple baffles located between the collectorand an output of the extreme ultraviolet light chamber. At least a firstportion of each one of the baffles is substantially aligned to anirradiation region and at least a second portion of at least one of theplurality of baffles is substantially not aligned to the irradiationregion.

Another embodiment provides a method of generating an extremeultraviolet light including outputting droplets of target material froma droplet generator in an extreme ultraviolet laser chamber, focusing asource laser on a selected one of the droplets in an irradiation region,irradiating the selected one of the droplets, collecting an extremeultraviolet light emitted from the irradiated droplet in a collector, areflective surface of the collector is cooled, a target material residueis deposited on the reflective surface of the collector, the targetmaterial residue being emitted from the irradiated droplet, a hydrogencontaining gas is injected into the extreme ultraviolet laser chamberand a first quantity of target material residue on the reflectivesurface of the collector is converted to a hydride and the hydride ofthe first quantity of target material residue is evaporated from thereflective surface of the collector, the evaporated hydride of the firstquantity of target material residue is removed from the extremeultraviolet laser chamber.

The method can also include collecting a second quantity of targetmaterial residue on a set of baffles located between the collector andan output of the extreme ultraviolet laser chamber. The method can alsoinclude heating at least a portion of the baffles to a meltingtemperature of the target material residue. The liquefied targetmaterial residue can be captured in a target material condenser system.

The method can also include heating non-critical inner surfaces of theextreme ultraviolet laser chamber to a temperature greater than thetemperature of the reflective surface of the collector. The non-criticalinner surfaces of the extreme ultraviolet laser chamber include surfacesother than the collector. Removing the evaporated hydride of the firstquantity of target material residue from the extreme ultraviolet laserchamber can include decomposing the evaporated hydride on the heatednon-critical inner surfaces of the extreme ultraviolet laser chamber.

The method can also include heating non-critical inner surfaces of theextreme ultraviolet laser chamber to a temperature equal to or greaterthan a melting temperature of the target material residue. The liquefiedtarget material residue can be captured in a target material condensersystem.

Still another embodiment provides a method of generating an extremeultraviolet light including outputting droplets of target material froma droplet generator in an extreme ultraviolet laser chamber, focusing asource laser on a selected one of the plurality of droplets in anirradiation region, irradiating the selected one of the plurality ofdroplets, collecting an extreme ultraviolet light emitted from theirradiated droplet in a collector and collecting a quantity of targetmaterial residue on a set of baffles located between the collector andan output of the extreme ultraviolet laser chamber.

Other aspects and advantages of the invention will become apparent fromthe following detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the principles ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be readily understood by the followingdetailed description in conjunction with the accompanying drawings.

FIG. 1 is a schematic view of a laser-produced-plasma EUV light source,in accordance with embodiments of the disclosed subject matter.

FIG. 2A is a schematic of the components of a simplified target materialdispenser that may be used in some or all of the embodiments describedherein in accordance with embodiments of the disclosed subject matter.

FIGS. 2B and 2C are more detailed schematics of some of the componentsin a EUV chamber in accordance with embodiments of the disclosed subjectmatter.

FIG. 3 is a flowchart diagram that illustrates the method operationsperformed in generating EUV, in accordance with embodiments of thedisclosed subject matter.

FIG. 4 is a flowchart diagram that illustrates the method operationsperformed in removing microparticles on the collector mirror, inaccordance with embodiments of the disclosed subject matter.

FIGS. 5A-5F illustrate a mid vessel baffle assembly in an EUV chamber,in accordance with an embodiment of the disclosed subject mater.

FIG. 6 illustrates a mid vessel baffle assembly in an EUV chamber, inaccordance with an embodiment of the disclosed subject matter.

FIG. 7 is a flowchart diagram that illustrates the method operationsperformed in capturing and removing the third portion of themicroparticles in the baffle assembly, in accordance with embodiments ofthe disclosed subject matter.

FIG. 8 is a block diagram of an integrated system including the EUVchamber, in accordance with embodiments of the disclosed subject matter.

DETAILED DESCRIPTION

Several exemplary embodiments for an improved catch system and methodfor capturing the unused droplets in an LPP EUV system will now bedescribed. It will be apparent to those skilled in the art that thepresent invention may be practiced without some or all of the specificdetails set forth herein.

One LPP technique involves generating a stream of target materialdroplets and irradiating some or all of the droplets with light pulses,e.g. zero, one or more pre-pulse(s) followed by a main pulse. In moretheoretical terms, LPP light sources generate EUV radiation bydepositing light or laser energy into a target material having at leastone EUV emitting element (e.g., xenon (Xe), tin (Sn) or lithium (Li)),creating a highly ionized plasma with electron temperatures of several10's of eV. The energetic radiation generated during de-excitation andrecombination of these ions is emitted from the plasma in alldirections.

A near-normal-incidence mirror (a “collector mirror”) is positioned at arelatively short distance (e.g., 10-50 cm) from the plasma to collect,direct and focus the EUV light to an intermediate location or focalpoint. The collected EUV light can then be relayed from the intermediatelocation to a set of scanner optics and ultimately to a target, such asa semiconductor wafer, in a photolithography process.

The collector mirror includes a delicate and relatively expensivemulti-layer coating to efficiently reflect EUV light. Keeping thesurface of the collector mirror relatively clean and protecting thesurface from unwanted plasma-generated debris is a challenge facing theEUV light source developers.

In an exemplary arrangement that is currently being developed with thegoal of producing about 100 W at the intermediate location. A pulsed,focused 10-12 kW CO₂ drive laser (or suitable other laser such as anexcimer laser) is synchronized with a droplet generator to sequentiallyirradiate about 10,000-200,000 tin droplets per second. This arrangementneeds to produce a stable stream of droplets at a relatively highrepetition rate (e.g., 10-200 kHz or more) and deliver the droplets toan irradiation site with high accuracy and good repeatability in termsof timing and position over relatively long periods of time.

FIG. 1 is a schematic view of a laser-produced-plasma EUV light source20, in accordance with embodiments of the disclosed subject matter. TheLPP light source 20 includes a light pulse generation system 22 forgenerating a train of light pulses and delivering the light pulses intoan EUV chamber 26. Each light pulse 23 travels along a beam path fromthe light pulse generation system 22 and into the EUV chamber 26 toilluminate a respective target droplet at an irradiation region 28.

Suitable lasers for use in the light pulse generation system 22 shown inFIG. 1, may include a pulsed laser device, e.g., a pulsed gas dischargeCO₂ laser device producing radiation at about 9.3 μm or about 10.6 μm,e.g., with DC or RF excitation, operating at relatively high power,e.g., about 10 kW or higher and high pulse repetition rate, e.g., about50 kHz or more. In one particular implementation, the laser in the lightpulse generation system 22 may be an axial-flow RF-pumped CO₂ laserhaving a MOPA configuration with multiple stages of amplification andhaving a seed pulse that is initiated by a Q-switched Master Oscillator(MO) with low energy and high repetition rate, e.g., capable of 100 kHzoperation. From the MO, the laser pulse may then be amplified, shaped,and focused before reaching the irradiation region 28.

Continuously pumped CO₂ amplifiers may be used for the light pulsegeneration system 22. For example, a suitable CO₂ laser device having anoscillator and three amplifiers (O-PA1-PA2-PA3 configuration) isdisclosed in co-owned U.S. Pat. No. 7,439,530, issued on Oct. 21, 2008,entitled, LPP EUV LIGHT SOURCE DRIVE LASER SYSTEM, the entire contentsof which are hereby incorporated by reference herein.

Alternatively, the laser in the light pulse generation system 22 may beconfigured as a so-called “self-targeting” laser system in which thedroplet serves as one mirror of the optical cavity. In some“self-targeting” arrangements, a master oscillator may not be required.Self targeting laser systems are disclosed and claimed in co-owned U.S.Pat. No. 7,491,954, issued on Feb. 17, 2009, entitled, DRIVE LASERDELIVERY SYSTEMS FOR EUV LIGHT SOURCE, the entire contents of which arehereby incorporated by reference herein.

Depending on the application, other types of lasers may also be suitablefor use in the light pulse generation system 22, e.g., an excimer ormolecular fluorine laser operating at high power and high pulserepetition rate. Other examples include, a solid state laser, e.g.,having a fiber, rod or disk shaped active media, a MOPA configuredexcimer laser system, e.g., as shown in U.S. Pat. Nos. 6,625,191,6,549,551, and 6,567,450, the entire contents of which are herebyincorporated by reference herein, an excimer laser having one or morechambers, e.g., an oscillator chamber and one or more amplifyingchambers (with the amplifying chambers in parallel or in series), amaster oscillator/power oscillator (MOPO) arrangement, a masteroscillator/power ring amplifier (MOPRA) arrangement, a poweroscillator/power amplifier (POPA) arrangement, or a solid state laserthat seeds one or more excimer or molecular fluorine amplifier oroscillator chambers, may be suitable. Other designs are possible.

Referring again to FIG. 1, the EUV light source 20 may also include atarget material delivery system 24, e.g., delivering droplets of atarget material into the interior of a chamber 26 to the irradiationregion 28, where the droplets 102A, 102B will interact with one or morelight pulses 23, e.g., one or more pre-pulses and thereafter one or moremain pulses, to ultimately produce a plasma and generate an EUV emission34. The EUV chamber 26 is maintained at a near vacuum (e.g., betweenabout 50 mT and 1500 mT) for the plasma formation. The target materialmay include, but is not necessarily limited to, a material that includestin, lithium, xenon, etc., or combinations thereof. The EUV emittingelement, e.g., tin, lithium, xenon, etc., may be in the form of liquiddroplets and/or solid particles contained within liquid droplets 102A,102B.

By way of example, the element tin may be used as pure tin, as a tincompound, e.g., SnBr₄, SnBr₂, SnH₄, as a tin alloy, e.g., tin-galliumalloys, tin-indium alloys, tin-indium-gallium alloys, or a combinationthereof. Depending on the material used, the target material may bepresented to the irradiation region 28 at various temperatures includingroom temperature or near room temperature (e.g., tin alloys, SnBr₄), atan elevated temperature, (e.g., pure tin) or at temperatures below roomtemperature, (e.g., SnH₄), and in some cases, can be relativelyvolatile, e.g., SnBr₄. More details concerning the use of thesematerials in an LPP EUV light source is provided in co-owned U.S. Pat.No. 7,465,946, issued Dec. 18, 2008, entitled ALTERNATIVE FUELS FOR EUVLIGHT SOURCE, the contents of which are hereby incorporated by referenceherein.

Referring further to FIG. 1, the EUV light source 20 includes acollector mirror 30. The collector mirror 30 is a near-normal incidencecollector mirror having a reflective surface in the form of a prolatespheroid (i.e., an ellipse rotated about its major axis). The actualshape and geometry can of course change depending on the size of thechamber and the location of focus. The collector mirror 30 can include agraded multi-layer coating in one or more embodiments. The gradedmulti-layer coating can include alternating layers of Molybdenum andSilicon, and in some cases one or more high temperature diffusionbarrier layers, smoothing layers, capping layers and/or etch stoplayers.

The collector mirror 30 also includes an aperture 32. The aperture 32allows the light pulses 23 generated by the light pulse generationsystem 22 to pass through to the irradiation region 28. The collectormirror 30 can be a prolate spheroid mirror that has a first focus withinor near the irradiation region 28 and a second focus at an intermediateregion 40. The EUV light 34 is output at or near the intermediate region40 from the EUV light source 20 and input to a device 42 utilizing EUVlight 34. By way of example, the device 42 that receives the EUV light34 can be an integrated circuit lithography tool.

It is to be appreciated that other optics may be used in place of theprolate spheroid mirror 30 for collecting and directing EUV light 34 toan intermediate location for subsequent delivery to a device utilizingthe EUV light. By way of example the collector mirror 30 can be aparabola rotated about its major axis. Alternatively, the collectormirror 30 can be configured to deliver a beam having a ring-shapedcross-section to the intermediate location 40 (e.g., co-pending U.S.patent application Ser. No. 11/505,177, filed on Aug. 16, 2006, entitledEUV OPTICS, the contents of which are hereby incorporated by reference).

The EUV light source 20 may also include an EUV controller 60. The EUVcontroller 60 can include a firing control system 65 for triggering oneor more lamps and/or laser devices in the light pulse generation system22 to thereby generate light pulses 23 for delivery into the chamber 26.

The EUV light source 20 may also include a droplet position detectionsystem including one or more droplet imagers 70. The droplet imagers 70can capture images using CCD's or other imaging technologies and/orbacklight stroboscopic illumination and/or light curtains that providean output indicative of the position and/or timing of one or moredroplets 102A, 102B relative to the irradiation region 28. The imagers70 are coupled to and output the droplet location and timing data to adroplet position detection feedback system 62. The droplet positiondetection feedback system 62 can compute a droplet position andtrajectory, from which a droplet error can be computed. The dropleterror can be calculated on a droplet by droplet basis or on averagedroplet data. The droplet position error may then be provided as aninput to the EUV controller 60. The EUV controller 60 can provide aposition, direction and/or timing correction signal to the light pulsegeneration system 22 to control a source timing circuit and/or tocontrol a beam position and shaping system to change the trajectoryand/or focal power or focal point of the light pulses being delivered tothe irradiation region 28 in the chamber 26.

The EUV light source 20 can also include one or more EUV metrologyinstruments for measuring various properties of the EUV light generatedby the source 20. These properties may include, for example, intensity(e.g., total intensity or intensity within a particular spectral band),spectral bandwidth, polarization, beam position, pointing, etc. For theEUV light source 20, the instrument(s) may be configured to operatewhile the downstream tool, e.g., photolithography scanner, is on-line,e.g., by sampling a portion of the EUV output, e.g., using a pickoffmirror or sampling “uncollected” EUV light, and/or may operate while thedownstream tool, e.g., photolithography scanner, is off-line, forexample, by measuring the entire EUV output of the EUV light source 20.

The EUV light source 20 can also include a droplet control system 90,operable in response to a signal (which in some implementations mayinclude the droplet error described above, or some quantity derivedtherefrom) from the EUV controller 60, to e.g., modify the release pointof the target material from a target material dispenser 92 and/or modifydroplet formation timing, to correct for errors in the droplets 102A,102B arriving at the desired irradiation region 28 and/or synchronizethe generation of droplets 102A, 102B with the light pulse generationsystem 22.

FIG. 2A is a schematic of the components of a simplified target materialdispenser 92 that may be used in some or all of the embodimentsdescribed herein in accordance with embodiments of the disclosed subjectmatter. The target material dispenser 92 includes a conduit or reservoir94 holding a fluid form of the target material 96. The fluid targetmaterial 96 can be a liquid such as a molten metal (e.g., molten tin),under a pressure, P. The reservoir 94 includes an orifice 98 allowingthe pressurized fluid target material 96 to flow through the orifice 98establishing a continuous stream 100. The continuous stream 100subsequently breaks into a stream of droplets 102A, 102B. The targetmaterial dispenser 92 further includes a sub-system producing adisturbance in the fluid having an electro-actuatable element 104 thatis operable, coupled with the fluid target material 96 and/or theorifice 98 and a signal generator 106 driving the electro-actuatableelement 104.

More details regarding various droplet dispenser configurations andtheir relative advantages may be found in co-pending U.S. patentapplication Ser. No. 12/214,736, filed on Jun. 19, 2008, entitledSYSTEMS AND METHODS FOR TARGET MATERIAL DELIVERY IN A LASER PRODUCEDPLASMA EUV LIGHT SOURCE; U.S. patent application Ser. No. 11/827,803,filed on Jul. 13, 2007, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCEHAVING A DROPLET STREAM PRODUCED USING A MODULATED DISTURBANCE WAVE;co-pending U.S. patent application Ser. No. 11/358,988, filed on Feb.21, 2006, entitled LASER PRODUCED PLASMA EUV LIGHT SOURCE WITHPRE-PULSE; co-owned U.S. Pat. No. 7,405,416, issued Jul. 29, 2008,entitled METHOD AND APPARATUS FOR EUV PLASMA SOURCE TARGET DELIVERY; andco-owned U.S. Pat. No. 7,372,056, issued on May 13, 2008, entitled LPPEUV PLASMA SOURCE MATERIAL TARGET DELIVERY SYSTEM; the contents of eachof which are hereby incorporated by reference.

The droplets 102A, 102B are between about 20 and about 100 μm indiameter. The droplets 102A, 102B are produced by pressurizing targetmaterial 96 through the orifice 98. By way of example, the orifice 98can have a diameter of less than about 50 μm in one embodiment. Thedroplets 102A, 102B are launched at a velocity of about 30 to 70 m/s.Due to the high velocity of the droplets 102A, 102B, the droplet stay onthe nearly straight droplet path 209 and do not impinge on the collectormirror 30, whether the droplets stream is produced in horizontal,vertical, or some other orientation. In one embodiment, not all thedroplets 102A, 102B produced by the target material dispenser 92 incontinuous mode are used for plasma generation. If the EUV source workswith a duty cycle of less than 100% a portion of the droplets 102 c willpass the irradiation region 28 and can be collected thereafter. If theunused droplets 102 c are allowed to impact the opposite wall of the EUVsource chamber they will produce a large amount of fast moving fragmentswith broad spatial distribution. Significant portions of these fragments231 will be deposited on the EUV collector mirror 30 and diagnosticports and devices 70, thus affecting their performance.

Another source of the debris is the irradiation region 28. Whenirradiated with intense light pulses the droplets 102A, 102B are heatedon one side that results in rapid asymmetric material expansion and EUVlight emissions 230. As described above the EUV light emissions 230 arecollected in the collector mirror 30. As a result of the expansion asignificant amount of droplet material is accelerated in the directionaway from the light pulse 23 with velocities comparable to the velocityof the droplets 102A, 102B as they are output from the target materialdispenser 92. This material is traveling away from the irradiationregion 28 until it strikes some surface, at which point it can bereflected or backsplashed in various directions. The backsplashed targetmaterial 231 may be deposited on the collector mirror 30.

FIGS. 2B and 2C are more detailed schematics of some of the componentsin a EUV chamber in accordance with embodiments of the disclosed subjectmatter. As described above, the target material dispenser 92 outputs astream of droplets 102A, 102B, however, not all of the droplets areirradiated (i.e., used) to generate the EUV 34. By way of example unuseddroplets 102C are not irradiated by the incoming light pulses 23.

The unused droplets 102C are captured in a first catch 210 so as tominimize any backsplash of the unused droplets within the EUV chamber26. The backsplash 236 can be in the form of microparticles or liquiddroplets. The unused droplets 102C strike the bottom 211 of the firstcatch 210. Microparticles 236 can reflect multiple times from the bottomand off the walls of first catch 210 and a portion of the microparticles 222, as shown in FIG. 2C, can escape back into the EUV chamber26 and a portion of the microparticles 231 can deposit on varioussurface such as on the collector mirror 30. Microparticles 220 are shownin phantom to illustrate some of the backsplash of microparticles thatare captured or prevented by the catch 210.

The first catch 210 can be an elongated tube having a cross section thatcan be circular, oblong, oval, rectangular, square, or any othersuitable shape. As shown in FIG. 2C, the first catch 210 includes anopen end 224 oriented toward the target material dispenser 92. The openend 224 can be substantially centered on the droplet path 209. The firstcatch 210 also includes a centerline 223 that may or may not be alignedto the droplet path 209 as will be described in more detail below.

The backsplash can be reduced or minimized by using a first catch 210having a relatively large aspect ratio L/W, e.g. greater than about 3and preferably greater than about 8, where L is the first catch lengthand W is the largest inside dimension normal to L, of the first catch.Upon striking the inner wall of the first catch 210, the unused droplets102 c reduce their velocity and the unused droplets can be captured inthe first catch, as shown.

As shown in FIG. 2B, the irradiated droplets can also producemicroparticles 232 after being irradiated. The microparticles 232 can bedistributed around the EUV chamber 26. A portion of the microparticles231 can be deposited on the collector mirror 30. A portion of themicroparticles 232 can be captured in an optional second catch 240. Thefirst catch 210 and second catch 240 can also be heated or cooled.

Parts, or all of the first and second catches 210, 240, may have doublewalls. The space between the double walls can be filled with, ordesigned to pass one or more heat exchange fluids, such as water, tin,gallium, tin-gallium alloy, etc., for the efficient thermal management(i.e., heating or cooling) of the catch 210, 240.

FIG. 3 is a flowchart diagram that illustrates the method operations 300performed in generating EUV 34, in accordance with embodiments of thedisclosed subject matter. The operations illustrated herein are by wayof example, as it should be understood that some operations may havesub-operations and in other instances, certain operations describedherein may not be included in the illustrated operations. With this inmind, the method and operations 300 will now be described.

In an operation 305, a light pulse 23 is directed to the irradiationregion 28 in the EUV chamber 26. In an operation 310, a selected one ofa stream of droplets 102A, 102B is delivered to the irradiation region28 at substantially the same time the light pulse 23 arrives at theirradiation region and EUV light 34 is generated from the irradiateddroplet in an operation 315.

In an operation 320, a first portion of microparticles 231, a secondportion of microparticles 232 and a third portion of microparticles 233are expelled from the irradiated droplet. The first portion of themicroparticles 231 are expelled out of the irradiation region 28 andtoward the collector mirror 30. The second portion of the microparticles232 are expelled out of the irradiation region 28 and toward the catches210, 240. The third portion of the microparticles 233 are expelled outof the irradiation region 28 and toward a secondary region 235B of theEUV chamber 26. The EUV chamber 26 is divided into a primary region 235Aand a secondary region 235B. The primary region 235A includes thecollector mirror 30 and the irradiation region 28. The secondary region235A includes that portion of the EUV chamber 26 between the outlet 40Aand the irradiation region 28.

In an operation 325, the second portion of the microparticles 232 andthe unused droplets 102C of the stream of droplets 102A, 102B arecaptured in the first and/or second catches 210, 240 as described above.Capturing the second portion of the microparticles 232 and the unuseddroplets 102C substantially limits any backsplash of microparticles anddroplets 236.

In an operation 330, the first portion of the microparticles 231 collecton the collector mirror 30. In an operation 335, the third portion ofthe microparticles 233 impact on any surfaces in the secondary region235B of the EUV chamber 26.

The third portion of the microparticles 233 is divided into a fourthportion 233A and a fifth portion 233B. In an operation 340, the fourthportion of the microparticles 233A impinge on and collect on thesurfaces 236A in the secondary region 235B of the EUV chamber 26. Thefifth portion of the microparticles 233B impinge on and reflect off thesurfaces 235A in the secondary region 235B of the EUV chamber 26 in anoperation 345. In an operation 350, the fifth portion of themicroparticles 233B eventually escape from the EUV chamber 26 though theoutlet 40A.

In an operation 355, the EUV from the irradiation region 28 is collectedby the mirror collector 30. The mirror collector 30 focuses the EUV 34to an intermediate location 40 in an operation 360 and in an operation365, the EUV 34 is output from the EUV chamber though the outlet 40A andthe method operations can end.

FIG. 4 is a flowchart diagram that illustrates the method operations 400performed in removing microparticles 231 on the collector mirror 30, inaccordance with embodiments of the disclosed subject matter. Theoperations illustrated herein are by way of example, as it should beunderstood that some operations may have sub-operations and in otherinstances, certain operations described herein may not be included inthe illustrated operations. With this in mind, the method and operations400 will now be described.

In an operation 405, an etchant and/or buffer gas is introduced into theEUV chamber 26. By way of example, Argon (Ar), Helium (He) and/orHydrogen (H) buffer gas can be included in the EUV chamber 26 to slowdown or stop the fast ions and microparticles 231 emitted by the plasmaso that the fast ions and microparticles 231 do not damage the collectormirror 30. Hydrogen and more particularly H radicals can be used forcleaning/etching of optical surfaces in the EUV chamber 26. The hydrogengas pressure inside the EUV chamber can be between about 300 to about800 mT and the gas flow into and out of the EUV chamber is between about50 and about 100 standard liters per minute (SLM).

In an operation 410, a light pulse 23 is directed to the irradiationregion 28 in the EUV chamber 26. In an operation 415, a selected one ofa stream of droplets 102A, 102B is delivered to the irradiation region28 at substantially the same time the light pulse 23 arrives at theirradiation region and a plasma is generated from the irradiated dropletin an operation 420. Irradiating the droplet generates target materialresidue including droplet fragments and microparticles 231, 232, 233 andfast moving ions emitted outward from the irradiation region 28.

In an operation 425, the buffer gas interacts with the plasma and thefast moving ions and the EUV light 34 photons and generates hydrogenradicals. In an operation 430, a first portion of microparticles 231including some fast moving ions are expelled from the irradiated dropletin the irradiation region 28 and toward the collector mirror 30. In anoperation 435, the first portion of microparticles 231 including somefast moving ions collects on the surface of the collector mirror 30thereby reducing the reflectivity of the collector mirror.

In an operation 440, the collector mirror 30 is cooled to less than thetemperature of the other inner surfaces of the EUV chamber. Thecollector mirror 30 is cooled to less about 50 degrees C. or cooler. Theformation and destruction of SnH4 is related to the temperature. Forhigher temperatures, the formation rate slows and the destruction rateincreases. Restated, tin on a hotter surface is less likely to bond withhydrogen to form SnH4 gas and SnH4 near a hot surface is more likely tobreakdown (i.e., decompose) into tin and hydrogen gas to deposit tin onthe hot surface and release the hydrogen as a hydrogen gas. Thus the tinremoval rate decreases as the collector mirror 30 temperature increases.Conversely, as the temperature of the collector mirror 30 is reduced theremoval of the deposited tin increases. Further, a higher relativetemperature of the remaining inner surfaces (e.g., vessel walls andbaffles) reduces tin removal from those surfaces. The differences intemperature between the cooler collector mirror 30 and the relativelyhotter vessel walls lead to tin transport from the cooler collectormirror 30 to the hotter vessel walls via SnH4. Possibly moreimportantly, this temperature differential substantially prevents tintransport from the vessel walls to the collector mirror 30 by SnH4.

By way of example, the collector mirror 30 can include a backsidecooling mechanism for cooling the backside of the collector mirror 30.The backside of the collector mirror 30 is opposite the side of thecollector mirror used for collecting and reflecting the EUV light 34.The backside cooling mechanism can include a cooling jacket 30A coupledto a cooling fluid source 30B for circulating a cooling fluid throughthe cooling mirror jacket 30A. Alternatively or additionally, a coolinggas flow 30C can be directed from a cooled gas source 30D toward thebackside of the collector mirror 30. Other suitable cooling mechanismsor combinations thereof can also be used.

In an operation 445, the hydrogen radicals react with target materialdeposits 231 on the surface of the collector mirror 30 and produce ahydride of the target material. By way of example if the target materialis tin, the hydrogen radicals for a tin-tetrahydride (SnH₄). The hydrideof the target material exits the surface of the collector mirror as agas in an operation 450. The hydride reaction proceeds faster atnon-elevated temperatures (e.g., less than about 50 degrees C.). Thereaction for tin target material is:Tin(solid)+hydrogen radical>>SnH₄(gas).

Referring again to the example of a tin containing target material inthe EUV chamber 26, the tin-tetrahydride (SnH₄) can absorb the EUV light34 and can decompose on surfaces in the EUV chamber thus redepositingtin. Therefore, reducing the quantity of the hydride of the targetmaterial in the EUV chamber 26 will improve the output of the EUV light34. In an operation 455, the non-critical surfaces in the EUV chamber 26are maintained at a temperature higher than the temperature of thecollector mirror 30 so as to promote the decomposition of the hydride ofthe target material and deposit the target material on the non-criticalsurfaces in an operation 460. The non-critical surfaces include thechamber walls 26A, 235A and other surfaces not including optical ordetectors.

By way of example, the non-critical surfaces 26A, 235A can be maintainedabove the melting point of the target material (e.g., above about 232degrees C. for tin target material). Maintaining the non-criticalsurfaces 26A, 235A above the melting point of the target material allowsliquid target material to form in an optional operation 465. The liquidtarget material can then be removed from the non-critical surfaces 26A,235A using gravity flow, wetting, etc. and out of the EUV chamber 26 ina target material condenser system 237, in an operation 470 and themethod operations can end.

As described above in operations 345 and 350 of FIG. 3, the fifthportion of the microparticles 233B impinge on and reflect off thesurfaces 235A in the secondary region 235B of the EUV chamber 26 andeventually escape from the EUV chamber 26 though the outlet 40A. Whenthe fifth portion of the microparticles 233B escape from the EUV chamber26 though the outlet 40A the fifth portion of the microparticles 233Bcan contaminate the subsequent process device 42 that uses the EUV light34. This contamination can be exacerbated when the EUV light path 246 isin a substantially vertical orientation and especially exacerbated whenthe EUV light path 246 is in a substantially vertical orientation andthe subsequent process device 42 is below the EUV chamber 26 such thatgravity assists the travel and escape of the fifth portion of themicroparticles 233B.

FIGS. 5A-5F illustrate a mid vessel baffle assembly 500 in an EUVchamber 26, in accordance with an embodiment of the disclosed subjectmater. FIG. 5A is schematic of a side view of the mid vessel baffleassembly 500. FIG. 5B is a more detailed schematic of a side view of themid vessel baffle assembly 500. FIG. 5C is a perspective view of the midvessel baffle assembly 500. FIG. 5D is side view of the mid vesselbaffle assembly 500. FIG. 5E is a sectional view of the mid vesselbaffle assembly 500. FIG. 5F is further detailed a schematic side viewof the mid vessel baffle assembly 500.

Referring first to FIG. 5A, the baffle assembly 500 is located in a midvessel region 235′ of the EUV chamber 26. The secondary region 235 ofthe EUV chamber 26 is divided into two portions: the mid vessel region235′ and an aft vessel region 235″. The mid vessel region 235′ begins atthe irradiation region 28 and extends toward the outlet 40A of the EUVchamber 26. The aft vessel region 235″ extends between the mid vesselregion 235′ and the outlet 40A of the EUV chamber 26. The mid vesselregion 235′ and the aft vessel region 235″ have no specific length andtherefore the mid vessel region 235′ can include substantially all ofthe secondary region 235 of the EUV chamber 26.

The baffle assembly 500 includes a series of passages and structures(described in more detail below) that receive, slow and capturesubstantially all of the third portion of the microparticles 233 createdwhen a droplet is irradiated in the irradiation region 28. The baffleassembly 500 can extend from the irradiation region 28 and the collectormirror 30 to the intermediate location 40 or any portion of thesecondary region 235 of the EUV chamber 26. While the baffle assembly500 can extend from the irradiation region 28 and the collector mirror30 to the intermediate location 40, the baffle assembly does not preventor otherwise occlude the EUV light 34 from passing from the collectormirror 30 through a three dimensional, cone-shaped transmissive region502 to the intermediate location 40.

The passages in the baffle assembly 500 begin at the edges 504A, 504B ofthe transmissive region 502 and the passages in the baffle assembly 500extend to the inner surfaces 235C of the EUV chamber 26. Exemplaryembodiments of the passages and the structures that form them in thebaffle assembly 500 are described in more detail below. Referring toFIG. 5C, the baffle assembly 500 is shown in a three dimensionalpictorial view. The baffle assembly 500 is a series of concentricbaffles 500A-500H surrounding but not protruding into the transmissiveregion 502. The baffle assembly 500 extends substantially from the edges504A, 504B of the transmissive region 502 to the inner surfaces 235C ofthe chamber.

Referring to FIGS. 5B and 5F, the baffle assembly 500 is shown in a sideview illustrating the series of concentric baffles 500A-500H. A firstportion of the baffles 500A, 500H are single step baffles and a secondportion of the baffles 500B-500G are multiple step baffles. The singlestep baffles 500A, 500H have an initial corresponding baffle angle αA,αH that is the same between the ends of the baffle assembly 500, nearthe edges 504A, 504B of the transmissive region 502 and the innersurfaces 235C of the EUV chamber 26. The initial corresponding baffleangle αA, αH can substantially align the single step baffles 500A, 500Hwith the irradiation region 28.

The single step baffles 500A are angled such that their attachment pointto the wall 235C of the EUV chamber is aligned with a shadow formed by afirst section of the adjacent baffle. Such an angle substantiallyprevents any direct line exposure of the wall by droplet fragmentscoming directly from the irradiation region 28. The droplet fragments(e.g., microparticles) therefore must first strike the first step in thebaffle, thus losing energy, before reaching the wall 235C. Reducing theenergy by deflecting the droplet fragments off at least one surface of abaffle before the droplet fragments impact the EUV chamber wall 235Creduces the possibility that the droplet fragment will deflect off ofthe EUV chamber wall and back toward the collector mirror 30. Further,any back deflection of the droplet fragment must then also bounce atleast once off a baffle surface before reaching the collector mirror 30,thus further reducing the energy and increasing the likelihood that thedroplet fragment will stick to the surface of the baffles 500A-500G andnot return to the collector mirror 30

The multiple step baffles 500B-500G have multiple corresponding baffleangles αB-αG and θB-θG such that the angle of the multiple step baffleschanges between the edges 504A, 504B of the transmissive region 502 andthe inner surfaces 235C of the EUV chamber 26. The corresponding initialbaffle angle αB-αG can be substantially align a corresponding firstportion 500B′-500G′ of the baffles 500A-500H with the irradiation region28, as shown by the phantom lines extending from the irradiation regiontoward each of the baffles 500A-500G. The corresponding second baffleangle θB-θG angles a corresponding second portion 500B″-500G″ of thebaffles 500A-500H away from the irradiation region 28 so as to promotereflection and capture of microparticles 233 emitted from theirradiation region.

It should be understood that while the baffles 500A-500H are shown asbeing straight and even multiple straight portions, a curved baffle501D-501H as shown in FIG. 5B could be used. The curvature of the curvedbaffles 501D-501H can vary between the edges 504A, 504B of thetransmissive region 502 and the inner surfaces 235C of the EUV chamber26. At least an initial portion of the curved baffles 501A-501H can besubstantially aligned with the irradiation region 28. A combination ofcurved and straight portions of the baffles could be used or acombination of straight and/or curved and/or multiple step baffles couldbe included in the baffle assembly 500. The baffles 500A-500H can besubstantially evenly spaced as shown in FIGS. 5C and 5E or unevenlyspaced as shown in FIGS. 5B and 5F.

One or more portions and/or one or more of the baffles 500A-500H can beheated or cooled as may be desired to improve the capture of themicroparticles 233 emitted from the irradiation region 28. The differentportions of the baffles 500A-500H can be manufactured of differentmaterials as may be desired for manufacturability, performance anddurability or other reasons. By way of example the baffles 500A-500H canbe manufactured from one or more of molybdenum, stainless steel (e.g.,SS-304, 316, Titanium, nickel, Copper or Aluminum or similar materials).

The baffle assembly 500 can also include holes or spaces or portions ofselected baffles removed to provide access for diagnostics detectors(e.g., EUV detectors), one or more pin-hole cameras, vacuum periscope,droplet imagining and detection and steering, target material catch,vacuum ports, windows and any other access needed for the access,design, construction and operation of the EUV chamber 26.

FIG. 6 illustrates a mid vessel baffle assembly 500 in an EUV chamber26, in accordance with an embodiment of the disclosed subject mater.FIG. 7 is a flowchart diagram that illustrates the method operations 700performed in capturing and removing the third portion of themicroparticles 233C in the baffle assembly 500, in accordance withembodiments of the disclosed subject matter. The operations illustratedherein are by way of example, as it should be understood that someoperations may have sub-operations and in other instances, certainoperations described herein may not be included in the illustratedoperations. With this in mind, the method and operations 700 will now bedescribed.

In an operation 705, a light pulse 23 is directed to the irradiationregion 28 in the EUV chamber 26. In an operation 710, a selected one ofa stream of droplets 102A, 102B is delivered to the irradiation region28 at substantially the same time the light pulse 23 arrives at theirradiation region and a plasma is generated from the irradiated dropletin an operation 715.

In an operation 720, the third portion of microparticles 233 (asdescribed in FIGS. 2B and 5A above) are emitted from the irradiationregion 28 toward the baffle assembly 500. The third portion ofmicroparticles 233 impinge on the baffle 500D″ and reflect at point 602toward the baffle 500E″, in an operation 725. In an operation 730, thethird portion of microparticles 233 are captured in the baffle assembly500 as the microparticles 233 reflect off point 604 and come to rest inthe space 605 between the baffle 500D″ and baffle 500E″.

In an optional operation 735, a portion of the baffle assembly 500and/or the EUV chamber can be heated. The portion of the baffle assembly500 and/or the EUV chamber can be heated such as with a heater 622. Theheater 622 can be any suitable heater by way of example the heater 622can be a resistive heater or a double wall jacket type heater orcombinations thereof. The heater 622 can be coupled to a heatercontrol/source 626 that can provide an electrical current to a resistiveheater 622 or a heated medium to circulate through the double jacketedheater 622.

In an operation 740, the accumulated microparticles 610 can be removedto a target material condenser system 237. Removing the accumulatedmicroparticles 610 can include heating the accumulated microparticles610 to a melting temperature and removing the accumulated microparticles610 in liquid form. The target material condenser system 237 can alsoinclude a vacuum source to draw the accumulated microparticles 610 insolid or liquid form into the target material condenser system 237through a withdrawal port 620.

FIG. 8 is a block diagram of an integrated system 800 including the EUVchamber 26, in accordance with embodiments of the disclosed subjectmatter. The integrated system 800 includes the EUV chamber 26, the lightpulse generation system 22, the device 42 utilizing output EUV light 34,and an integrated system controller 810 coupled to the EUV chamber, thelight pulse generation system and the device utilizing output EUV light.The integrated system controller 810 includes or is coupled to (e.g.,via a wired or wireless network 812) a user interface 814. The userinterface 814 provides user readable outputs and indications and canreceive user inputs and provides user access to the integrated systemcontroller 810.

The integrated system controller 810 can include a special purposecomputer or a general purpose computer. The integrated system controller810 can execute computer programs 816 to monitor, control and collectand store data 818 (e.g., performance history, analysis of performanceor defects, operator logs, and history, etc.) for the EUV chamber 26,the light pulse generation system 22 and the device 42. By way ofexample, the integrated system controller 810 can adjust the operationsof the EUV chamber 26, the light pulse generation system 22 and/or thedevice 42 and/or the components therein (e.g., the first catch 210and/or second catch 240, target material dispenser 92, baffle assembly500, etc.) if data collected dictates an adjustment to the operationthereof.

With the above embodiments in mind, it should be understood that theinvention may employ various computer-implemented operations involvingdata stored in computer systems. These operations are those requiringphysical manipulation of physical quantities. Usually, though notnecessarily, these quantities take the form of electrical or magneticsignals capable of being stored, transferred, combined, compared, andotherwise manipulated. Further, the manipulations performed are oftenreferred to in terms, such as producing, identifying, determining, orcomparing.

Any of the operations described herein that form part of the inventionare useful machine operations. The invention also relates to a device oran apparatus for performing these operations. The apparatus may bespecially constructed for the required purpose, such as a specialpurpose computer. When defined as a special purpose computer, thecomputer can also perform other processing, program execution orroutines that are not part of the special purpose, while still beingcapable of operating for the special purpose. Alternatively, theoperations may be processed by a general purpose computer selectivelyactivated or configured by one or more computer programs stored in thecomputer memory, cache, or obtained over a network. When data isobtained over a network the data maybe processed by other computers onthe network, e.g., a cloud of computing resources.

The embodiments of the present invention can also be defined as amachine that transforms data from one state to another state. Thetransformed data can be saved to storage and then manipulated by aprocessor. The processor thus transforms the data from one thing toanother. Still further, the methods can be processed by one or moremachines or processors that can be connected over a network. Eachmachine can transform data from one state or thing to another, and canalso process data, save data to storage, transmit data over a network,display the result, or communicate the result to another machine.

The invention may be practiced with other computer system configurationsincluding hand-held devices, microprocessor systems,microprocessor-based or programmable consumer electronics,minicomputers, mainframe computers and the like. The invention may alsobe practiced in distributing computing environments where tasks areperformed by remote processing devices that are linked through anetwork.

The invention can also be embodied as computer readable code on acomputer readable medium. The computer readable medium is any datastorage device that can store data, which can thereafter be read by acomputer system. Examples of the computer readable medium include harddrives, network attached storage (NAS), read-only memory, random-accessmemory, CD-ROMs, CD-Rs, CD-RWs, DVDs, Flash, magnetic tapes, and otheroptical and non-optical data storage devices. The computer readablemedium can also be distributed over a network coupled computer systemsso that the computer readable code is stored and executed in adistributed fashion.

It will be further appreciated that the instructions represented by theoperations in the above figures are not required to be performed in theorder illustrated, and that all the processing represented by theoperations may not be necessary to practice the invention.

Although the foregoing invention has been described in some detail forpurposes of clarity of understanding, it will be apparent that certainchanges and modifications may be practiced within the scope of theappended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the invention is notto be limited to the details given herein, but may be modified withinthe scope and equivalents of the appended claims.

What is claimed is:
 1. A chamber comprising: a first surface disposedwithin the chamber; a cooling system coupled to operative to maintainthe first surface to less than a melting temperature of a targetmaterial; a target material dispenser system containing a quantity ofthe target material, the target material dispenser capable of flowingthe target material to an irradiation region in the chamber, a firstportion of the target material being deposited on at least a portion ofthe first surface; a hydrogen containing gas source coupled to thechamber; and a hydrogen radical generator including a target materialplasma capable of being formed by irradiating the target material at theirradiation region, the target material plasma capable of generatinghydrogen radicals from the hydrogen containing gas source, the hydrogenradicals being capable of reacting with the first portion of targetmaterial deposited on the first surface to form a volatile hydride ofthe target material.
 2. The chamber of claim 1, wherein irradiating thetarget material at the irradiation region includes irradiating thetarget material with at least one light pulse.
 3. The chamber of claim1, wherein hydrogen radical generator includes the target materialplasma and an EUV light source, wherein the hydrogen containing gasinteracts with the target material plasma and EUV light photons togenerate hydrogen radicals.
 4. The chamber of claim 1, wherein the firstsurface disposed within the chamber includes a light reflective surface.5. The chamber of claim 1, further comprising an inner surface of atleast one wall of the chamber.
 6. The chamber of claim 1, furthercomprising a second surface including at least a first portion of aplurality of baffles disposed within the chamber.
 7. The chamber ofclaim 6, wherein each of the plurality of baffles being in contact withan inner surface of the chamber.
 8. The chamber of claim 6, wherein theplurality of baffles disposed within the chamber are disposed proximateto an outlet of the chamber.
 9. The chamber of claim 6, wherein thefirst portion of the plurality of baffles begin at an edge of atransmissive region.
 10. The chamber of claim 1, further comprising aheat source coupled to a third surface disposed within the chamber,wherein the heat source is capable of heating the third surface withoutheating the first surface.
 11. The chamber of claim 10, wherein the heatsource is capable of heating at least a portion of the third surface toa temperature greater than the first surface without heating the firstsurface.
 12. The chamber of claim 10, wherein the heat source is capableof heating at least a portion of the third surface to at least a meltingtemperature of a target material.
 13. A chamber comprising: a lightreflective first surface disposed within the chamber; a cooling systemcoupled to operative to maintain the first surface to less than amelting temperature of a target material; a target material dispensersystem containing a quantity of the target material, the target materialdispenser capable of flowing the target material to an irradiationregion in the chamber, a first portion of the target material beingdeposited on at least a portion of the first surface; a hydrogencontaining gas source coupled to the chamber; a hydrogen radicalgenerator including a target material plasma capable of being formed byirradiating the target material at the irradiation region, the targetmaterial plasma capable of generating hydrogen radicals from thehydrogen containing gas source, the hydrogen radicals being capable ofreacting with the first portion of target material deposited on thefirst surface to form a volatile hydride of the target material; and aheat source coupled to a second surface disposed within the chamber,wherein the heat source is capable of heating the second surface withoutheating the first surface.
 14. A method of removing residue from asurface comprising: maintaining a first surface to less than a meltingtemperature of a target material the first surface being disposed withina chamber; flowing the target material to an irradiation region in thechamber; irradiating the target material at the irradiation region toform a target material plasma; depositing a first quantity of the targetmaterial on the first surface; injecting a hydrogen containing gas intothe chamber; generating hydrogen radicals from the hydrogen containinggas within the chamber, wherein the target material plasma generates thehydrogen radicals; converting a first portion of the first quantity oftarget material on the first surface to a hydride, wherein the hydrogenradicals react with the first portion of the first quantity of targetmaterial to form the hydride; and evaporating the hydride of the firstportion of the first quantity of target material residue from the firstsurface; and removing the evaporated hydride of the first portion of thefirst quantity of target material residue from the chamber.
 15. Themethod of claim 14, further comprising collecting a second quantity oftarget material residue on at least a second portion of a plurality ofbaffles disposed within the chamber.
 16. The method of claim 15, furthercomprising heating a second portion of the plurality of baffles to amelting temperature of the second quantity of target material residuewithout heating the first surface.
 17. The method of claim 16, furthercomprising capturing the melted second quantity of target materialresidue in a target material condenser system.
 18. The method of claim14, wherein removing the evaporated hydride of the first quantity oftarget material residue from the chamber includes decomposing theevaporated hydride on a plurality of non-critical inner surfaces of thechamber.
 19. The method of claim 14, further comprising heating aplurality of non-critical inner surfaces of the chamber to a temperatureequal to or greater than a melting temperature of the target materialresidue, the plurality of non-critical inner surfaces of the chamberinclude surfaces other than the first surface.